Isolated cold plate refrigeration system with user selected temperature control

ABSTRACT

An isolated cold plate refrigeration system provides a cargo compartment isolated from a cold plate compartment. A user defines the target temperature of the cargo compartment. When the temperature of the cargo compartment rises above the target temperature and cool air is required to reduce the temperature of the cargo compartment, a cold plate fan is activated to move air from the cold plate compartment to the cargo compartment and from the cargo compartment to the cold plate compartment.

FIELD OF THE INVENTION

This invention is generally directed to a refrigeration system for a vehicle which utilizes isolated eutectic cold plates to provide and maintain a temperature controlled compartment at a user selected target temperature.

BACKGROUND OF THE INVENTION

Current vehicle refrigeration systems utilize eutectic cold plates to keep goods cool during transportation by placing the cold plates within the cargo compartment. These eutectic cold plates are frozen or charged prior to use, are positioned inside the cargo compartment, and are designed to absorb heat in order to maintain the cargo compartment at a constant temperature throughout the course of the delivery route. Although minimized due to the insulation provided, when the ambient temperature is higher than that of the cargo compartment, heat is gained within the cargo compartment from the exterior of the cargo compartment, through the insulated walls. In addition, as stops are made along the route and the cargo compartment is opened in order to access the cargo compartment, the cold plates are exposed to the ambient air, resulting in depletion of the cold plates.

Because the temperature at which different types of goods to be stored varies, different types of cold plates are provided to deliver these temperatures. For example, “medium” temperature cold plates will be utilized for goods which are to be stored at a “medium” temperature, “low” temperature cold plates will be utilized for goods which are to be stored at a “low” temperature, and “deep freeze” plates will be utilized for goods which are to be stored at a “deep freeze” temperature. Once charged, the cold plates maintain these temperatures until the cold plates are depleted. Once fully depleted, the vehicle is returned to its home base and the cold plates are re-charged.

As noted above, different types of cold plates provide the ability to maintain the cargo area at different temperatures. Thus, the cold plate used to cool the cargo compartment must be matched with the goods to be transported. In the event a single vehicle is to be used to transport goods at various temperatures, multiple cargo compartments can be utilized. Each cargo compartment contains a cold plate selected in accordance with the particular temperature requirements. As described in U.S. Pat. No. 6,543,245 to Waldschmidt et al., if desired, a single compressor system is used to maintain the temperature of multiple cargo compartments and cold plates.

Once the cold plate is positioned within the cargo compartment and charged for use, the temperature of the cargo compartment is fixed within the range permissible by the selected cold plate. Currently available systems therefore, do not allow the user to select the temperature of the cargo compartment as needed.

The present invention provides an isolated cold plate refrigeration system which overcomes the problems presented in the prior art and which provides additional advantages over the prior art, such advantages will become clear upon a reading of the attached specification in combination with a study of the drawings.

SUMMARY OF THE INVENTION

Briefly, the present invention discloses a cold plate refrigeration system wherein the cold plate is provided in a cold plate compartment which is isolated from the cargo compartment. Cooling of the cargo compartment is achieved by performing a cold plate air exchange operation to draw air from the cargo compartment across the cold plates in the cold plate compartment and back to the cargo compartment. In this manner, the temperature of the cargo compartment can be controlled as desired by the user.

BRIEF DESCRIPTION OF THE DRAWINGS

The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which:

FIG. 1 illustrates a vehicle in which an embodiment of the isolated cold plate refrigeration system of the present invention is utilized with a portion of the vehicle body removed to illustrate the location of components of the system;

FIG. 2 is a diagram illustrating an embodiment of the isolated plate refrigeration system and;

FIG. 3 is a block diagram illustrating operation of the controller utilized in the systems of FIG. 2 and FIG. 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, a specific embodiment with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein.

The isolated cold plate refrigeration system of the present invention is designed for use in a vehicle 10 for transporting refrigerated goods as shown in FIG. 1. The vehicle 10 generally includes a cab 12 which houses the engine 14 and a transmission 16 and a body 18 for transporting goods. The body 18 generally includes a pair of rectangular sidewalls 20 (the right side wall 20 being shown), a front wall 22, a rear wall 24, a roof structure 26, a floor structure 28, and a compartment access door 30. The floor structure 28 is supported by an under carriage assembly 32. The body 18 generally defines a temperature controlled cargo compartment 34 and a cold plate compartment 36.

The body 18 of the vehicle 10 which provides the isolated cold plate refrigeration system 50 is illustrated in FIG. 2. An isolation wall 52 is provided within the body 18 of the vehicle 10 and is positioned between the temperature controlled cargo compartment 34 and the cold plate compartment 36. The cargo compartment 34 generally extends from the isolation wall 54 to the rear wall 30 of the body 18 and the cold plate compartment 36 generally extends from the isolation wall 52 to the front wall 22 of the body 18.

The temperature controlled cargo compartment 34 is typically used to house goods to be maintained at a designated target temperature which is typically lower than the ambient temperature. The cargo compartment 34 is defined by a portion of the interior surfaces 20 a of the side walls 20, the interior surface 30 a of the rear wall 30, a portion of the interior surface of the roof structure 26, a portion of the interior surface 28 a of the floor structure 28 and a rear surface 52 a of the isolation wall 52. The sidewalls 20, the rear wall 30, the roof structure 26, the floor structure 28 and the isolation wall 52 are provided by insulated walls designed to maintain the internal temperature of the cargo compartment 34. A recirculation fan 54 and a temperature sensor 56 are positioned within the cargo compartment 34.

A cargo compartment access door 58 is provided in the rear wall 30 to provide access to the cargo compartment 34 and to allow for loading and unloading of goods to and from the cargo compartment 34. A cargo compartment access door switch 60 is provided in communication with the cargo compartment access door 58.

An evaporator system 62 is provided in communication with the cargo compartment 34. The evaporator system 62 can be, for example, a typical evaporator system 62 commonly used in connection with a refrigeration vehicle. The evaporator system includes a compressor, a condenser, and an expansion valve (not shown).

A heater system 64 is provided in communication with the cargo compartment 34. The heater system 64 can be, for example, a resistive electric heater system such as those typically used in connection with a refrigeration vehicle for increasing the temperature of the cargo compartment 34 when necessary.

The isolation wall 52 extends at its upper end 66 to the interior surface 26 a of the roof structure 26 and at its lower end 68 to the interior surface 28 a of the floor structure 28. The isolation wall 52 also extends from the interior surface 20 a of the left side wall 20 to the interior surface 20 a of the right side wall 20. The isolation wall 52 defines a first passageway 70 positioned proximate the upper end 66 of the isolation wall 52 and a second passageway 72 positioned proximate a lower end 68 of the isolation wall 52. A first passage covering 73 is provided in connection with the first opening and provides the ability to open or close the first passageway 70. The first passageway covering 73 can be provided by, for example, a door or a curtain. Alternatively, as shown in FIG. 2, the first passageway covering 73 is provided in connection with the cold plate fan 76 as will be described herein. A second passageway covering 74 is provided in connection with the second passage 72 and provides the ability to open or close the second passageway 72. The second passageway covering 72 can be, for example, a hinged door or a curtain. A cold plate fan 76 is provided in connection with the first passageway 70 of the isolation wall 52. The cold plate fan 76 includes the first passageway covering 73 which closes the opening 70 when the fan is not in use. The cold plate fan 76 can be either a single speed fan or a variable speed fan.

The cold plate compartment 36 houses a cold plate 80. The cold plate compartment 36 is defined by the interior surface 22 a of the front wall 22, a portion of the interior surfaces of the side walls 20, a portion of the interior surface 26 a of the roof structure 26, a portion of the interior surface 28 a of the floor structure 28, and the front surface 52 b of the isolation wall 52. Baffles 82 are provided on interior surface 22 a of the front wall 22 and on the front surface 52 b of the isolation wall 52.

The cold plate 80 is mounted within the cold plate compartment 36 and is spaced from the interior surface 22 a of the front wall 22 of the body 18 and is spaced from the front surface 52 b of the isolation wall 52. The cold plate 80 is preferably a low temperature type cold plate.

A defrost system 81 is provided in connection with the cold plate 80. The defrost system generally includes a defrost tube 84, a heater 86, and a pump 88. The defrost tube 84 is positioned in serpentine pattern on opposite surfaces 80 a,80 b of the cold plate 80. The defrost tube 84 preferably has a rectangular cross-section. The defrost tube 84 is in communication with the pump 88 and the heater 86 and is filled with a water/ethylene glycol mixture.

A controller 90 is provided for the purpose of sending and receiving various signals from various components of the isolated cold plate refrigeration system 50 and for providing signals to the various components. The controller 90 is therefore in electrical communication with the temperature sensor 56, the re-circulation fan 54, the cargo compartment access door switch 60, the evaporator system 62, the heater system 64, the cold plate fan 76, the first door 73, the second door 74, and the defrost system 81.

Power for operation of the isolated cold plate refrigeration system 50 can be provided via known methods including sourcing power from the utility grid while the vehicle is at its home base, sourcing power from a generator driven by the vehicle engine, sourcing power from an auxiliary generator which is independent of the engine driven generator, or sourcing power from the vehicle's electrical system. Criteria for sourcing power from these various sources so as to maximize cost and energy efficiency are well known and will not be described herein. Alternatively power to the isolated cold plate refrigeration system can be provided in accordance with Applicant's new integrated power system described in the patent application concurrently filed by Applicant titled Integrated Power System for a Vehicle Accessory, the disclosure of which is herein incorporated by reference.

Operation of the refrigeration system is as follows. Prior to beginning a delivery or pickup route, the isolated cold plate refrigeration system 50 is prepared for use at the vehicle's home base. The target temperature of the cargo compartment 34 is provided to the controller 90. Power from the utility grid is utilized to charge the cold plate 80. The eutectic temperature of the cold plate 80 is selected to be substantially lower than the user selected target temperature. If desired, the evaporator system 62 may also be powered from the utility grid and operated to reduce and maintain the temperature of the cargo compartment 34. The cold plate 80 is brought to eutectic condition using shore power.

Typically the ambient temperature is higher than the target temperature of the cargo compartment 34 and after the cargo compartment 34 is loaded with the goods to be delivered the isolated cold plate refrigeration system 50 is utilized to cool and maintain the temperature of the cargo compartment 34 at the target temperature as will be described herein. As the cargo compartment 34 is loaded with the goods, shore power is used to operate the evaporation system 62 in order to maintain the temperature of the cargo compartment 34. Once the cargo compartment 34 has been loaded with the goods to be delivered, the shore power is disconnected from the refrigeration system 50 and the vehicle 10 may begin its travels.

As the truck begins it travels, the compartment re-circulation fan 54 will operate to continuously move air within the cargo compartment 34 so as to provide a consistent temperature throughout the cargo compartment 34. When the ambient temperature is warmer than the target temperature of the cargo compartment, the temperature within the cargo compartment 34 will begin to rise. The temperature sensor 56 continuously measures and provides temperature data to the controller 90. When the temperature data provided to the controller 90 indicates a need to cool the cargo compartment 34, i.e. when the temperature rises sufficiently above the target temperature, the controller 90 in response provides a signal to begin a cold plate air exchange operation.

The cold plate air exchange operation provides that the first door 73 and second door 74 of the isolation wall 52 are opened and the cold plate fan 76 is turned on so as to draw warm air from the cargo compartment 34 into the cold plate compartment 36. The first door 73 and second door 74 can be opened as a result of a mechanical control which receives a signal from the controller 90. Alternatively, passive doors are provided which open in response to the flow of air initiated by the cold plate fan 76. During the cold plate air exchange operation, air is moved across the cold plate 80 as indicated by the arrows 92. As the air is drawn past the cold plate 80, the air is cooled and is re-circulated back to the cargo compartment 34 through the use of the cold plate fan 76. This process continues until the temperature of the cargo compartment 34 reaches the target temperature. If the cold plate fan 76 is provided by a variable speed fan, the controller 90 provides a speed control signal to the cold plate fan 76 to determine the rate at which the fan 76 draws air across the cold plate 80. By increasing the speed of the fan 76, a greater volume of air will be drawn across the cold plate 80 in a particular time frame and therefore will provide a greater volume of cool air to the cargo compartment 34. Thus, in event a number of door openings have occurred or if the ambient temperature is relatively high, the fan 76 can be operated at a high speed. On the other hand, in the event the cargo compartment 34 has not been accessed or the ambient temperature is relatively close to the target temperature, a lower volume of air is required to be drawn across the cold plate 80 and the variable speed fan 76 can be operated at a lower speed. Alternatively, if a single speed fan 76 is used, the volume of air drawn across the cold plate 80 can be varied by varying the duration of time for which the cold plate fan 76 is in operation.

Once the cargo compartment 34 has reached the target temperature the first door 73 and second door 74 are closed to isolate the cold plate compartment 36 from the cargo compartment 34 and the re-circulation fan 54 is again activated to provide circulation of the air through out the cargo compartment 34.

During the cold plate air exchange operation, therefore, the first door 73 and second door 74 are opened and air is drawn from the cold plate compartment 36 into the cargo compartment 34. When the cold plate air exchange operation is completed the first door 73 and second door are closed to seal the first and second passageway preventing the flow of air between the cold plate compartment 36 and the cargo compartment 34 and therefore isolating the cold plate compartment 36 from the cargo compartment 34.

When the truck reaches a destination, the cargo compartment access door 58 will be opened in order to access the goods to be delivered. When the operator opens the cargo compartment access door 58, the door switch 60 is activated to provide a door open signal to the controller 90. Upon receipt of the door open signal, a response signal is provided from the controller 90 to the compartment re-circulation fan 54 to ensure that if the re-circulation fan 54 is on, the re-circulation fan 54 is then turned off. This will ensure that excess air from the cargo compartment 34 does not escape the cargo compartment 34 when the door is opened. In addition, a signal is provided to the cold plate fan 76 to ensure that if the cold plate fan 76 is on, the cold plate fan 76 is turned off. If first door 73 and second door 74 are operated via controller 90, signals are provided from the controller 90 to close the first door 73 and second door 74 of the isolation wall 52. Alternatively, if first door 73 and second door 74 are provided by passive doors, the first and second doors will close as a result of the cold plate fan 76 being in an off condition. This process will ensure that if the refrigeration system 50 was in the midst of a cold plate air exchange process, this process is interrupted when the access door is opened. By closing the first door 73 and second door 74 of the isolation wall 52, the cold plate 80 will remain insulated from the cargo compartment 34 while the cargo compartment access door 58 is open, thereby preventing an excess of warm air from being drawn into the cold plate compartment 36. By isolating the cold plate in this manner when the cargo compartment access door is opened, excessive depletion of the cold plate is avoided. With the cargo compartment access door 58 open, the operator may remove goods from or provide goods to the cargo compartment 34.

Upon completion of the removal or loading of goods, the operator will close the cargo compartment access door 58 and the cargo compartment door switch 60 will provide a cargo compartment door closed signal to the controller 90. Upon receipt of the cargo compartment door closed signal, the compartment re-circulation fan 54 will resume operation. In addition, the evaporator system 62 will be activated to reduce the temperature of the cargo compartment 34. Preferably, the evaporator system 62 is employed prior to a cold plate exchange process in order to avoid depletion of the cold plate 80.

As the vehicle progresses through its delivery and loading schedule, the cold plate air exchange operation will be intermittently used to maintain the temperature of the cargo compartment 34 at the target temperature. In addition, the evaporation system 62 will intermittently be employed to re-charge the cold plate 80 as necessary. The re-charging of the cold plate provides for extended use of the cold plate 80 and therefore provides for extended use of the refrigeration vehicle.

Once the delivery or pick-up route is complete, the vehicle is returned to its home base and can again be connected to the utility grid through a shore power connection.

As a result of the cold plate air exchange operations, frost will accumulate on the cold plate surfaces and a frost sensor provides a frost signal to the controller 90 indicating that an accumulation of frost has formed on the cold plate 80. Because the frost acts as an insulation barrier, the heat transfer efficiency of the cold plates is diminished when frost has accumulated. Thus, with the vehicle 10 at the home base and connected to shore power, when the frost signal indicating that an accumulation of frost is present on the cold plate 80 is provided to the controller 90, the controller 90 in response provides a signal to activate the defrost system 81. Upon activation, the defrost heater 86 will heat the water/ethylene glycol mixture and the pump 88 will circulate the heated mixture through the defrost tube 84 to defrost the cold plate 80. Once the cold plate 85 has been defrosted, the cold plate 80 can be recharged during the connection to the utility grid to prepare the refrigeration system for the next route. In addition, if desired, the temperature of the cargo compartment can be maintained at the target temperature through operation of the evaporator system 62.

Operation of the logic provided by the controller 90 is illustrated in FIG. 3. At step 100 the user sets the target temperature of the cargo compartment. At step 102 the controller determines whether the isolated cold plate refrigeration system is connected to utility grid power through a shore power connection. If the system is connected to the utility grid, at step 104 the controller determines if the cold plate 80 need does to be defrosted. If the controller 90 determines that a defrosting of the cold plate 80 is needed a defrost operation is initiated at step 106. Once it has been determined that the defrost operation is complete at step 108, the controller determines if the cold plate 80 needs to be recharged at step 110. Alternatively, if the controller determines at step 104 that the cold plate 80 does not need to be defrosted, the controller proceeds to step 110. If at step 110, it is determined that the cold plate 80 needs to be recharged, the cold plate 80 recharge operation is activated at step 112, and the controller 90 proceeds to step 114 to determine if the cold plate recharge operation is complete. If on the other hand at step 110, it is determined that the cold plates do not need to be charged, the controller 90 will measure the temperature of the cargo compartment 34 at step 116. Alternatively, if at step 102 it is determined that the system 50 is not connected to the utility grid, the controller 90 will proceed to step 116 and measure the temperature of the cargo compartment 34.

At step 118 the controller will determine whether the temperature of the cargo compartment 34 is at the target temperature. The controller is provided with a plurality of set points, such as for example, a heater activation set point, an evaporator activation set point, and a cold plate activation set point. These set points are utilized for performing a temperature hysteresis function. If at step 118 it is determined that the cargo compartment is not at the target temperature, the controller 90 determines whether the temperature of the cargo compartment is too high or too low at step 120. If at step 120 it is determined that the temperature of the cargo compartment 34 is too low, at step 122 the controller determines whether the temperature of the cargo compartment is below the heater activation set point. If the temperature of the cargo compartment is below the heater activation set point, at step 124, the heater is activated and operated until the target temperature exceeds the heater activation set point by, for example, two degrees (2°). If at step 122 is determined that the temperature of the cargo compartment is not below the heater activation set point, the controller returns to step 116 and continues to monitor the temperature of the cargo compartment.

If at step 120 it is determined that the temperature of the cargo compartment is too high, the controller 90 at step 126, determines whether the cargo compartment access door 58 is open. If at step 126 it is determined that the cargo compartment access door 58 is opened, the controller 90 at step 128 monitors whether a door closed signal has been received. Once the door closed signal has been received or alternatively if at step 126 it has been determined that the door 58 is not open, the controller 90 at step 130 determines whether the temperature of the cargo compartment is above the evaporation activation set point.

If the temperature of the cargo compartment is not above the evaporator activation set point, the controller at step 132 determines whether the temperature of the cargo compartment exceeds the cold plate activation set point. If at step 132 it is determined that the temperature of the cargo compartment does not exceed the cold plate activation set point, the controller returns to step 116 where the cargo compartment temperature is monitored. If at step 132 it is determined that the temperature of the cargo compartment exceeds the cold plate activation set point, at step 134 the cold plate air exchange operation is activated and performed until the temperature is one degree (1°) below the target temperature.

If at step 130 it is determined that the temperature of the cargo compartment is above the evaporator activation set point, at step 136 the evaporator is activated and operated until the temperature of the cargo compartment is at least two degrees (2°) below the target temperature.

As described, the refrigeration system 50 allows the user to select the target temperature. By isolating the cold plate 80 from the cargo compartment 34, the target temperature of the cargo compartment 34 can be realized without requiring the type of cold plate 80 to be matched to the cargo compartment 34. Isolation of the cold plates 80 provides the ability to control delivery of cool air by transfer of heat from the cargo compartment 34 to the cold plates 80 and transfer of cool air from the cold plate compartment 36 to the cargo compartment 34. Recirculation of the air in this manner provides a closed loop which provides for control of the cargo compartment temperature. If desired, therefore, the user can en-route change the target temperature of the cargo compartment 34. If, for example, the vehicle's route requires that a first supply of goods requiring a medium temperature be delivered to a first location and a second supply of goods requiring a low temperature be picked up from the first location and delivered to a second location, the target temperature of the cargo compartment 34 can be adjusted to meet these requirement. Initially, the controller will be provided with the medium target temperature. After delivery of the first supply of goods, the controller is provided with the low target temperature and the second supply of goods is loaded in the cargo compartment 54.

While preferred embodiments of the present invention are shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.

If desired, multiple cargo compartments can be provided for simultaneous transport of goods at different target temperatures. In this scenario, each cargo compartment will have an independently selected target temperature. The target temperature of each cargo compartment 34 can be controlled by controlling the flow of air from the cold plate compartment 36 to each cargo compartment 34. For example, the vehicle may provide a low temperature cargo compartment and a medium temperature cargo compartment. The low temperature cargo compartment includes a warm air passageway from the low temperature cargo compartment to the cold plate compartment 36 and a first cold plate fan 66 can be utilized to provide cooled air from the cold plate compartment 36 to the low temperature cargo compartment. The medium temperature compartment includes a warm air passageway from the medium temperature compartment to the cold plate compartment 36 and a second cold plate fan 66 can be utilized to provide cooled air from the cold plate compartment 36 to the medium temperature cargo compartment. Alternatively, a single cold plate fan 66 can be utilized to draw air passed the cold plate 80 and a cold air passageway can be configured to deliver the cold air to either the low temperature cargo compartment or the medium temperature cargo compartment independently or both compartments simultaneously.

Although the isolated cold plate refrigeration system 50 has been described as including an evaporator system 62, it is to be understood that inclusion of the evaporator system 62 is not necessary for operation of the isolated cold plate refrigeration system 50. In the event an evaporation system 62 is not provided, cooling of the cargo compartment 34 will be achieved solely through the cold plate air exchange operation, while the vehicle is in operation. In addition, recharging of the cold plate 80 through the evaporation system 62 would not be available. Recharging of the cold plate 80 would occur, therefore, when the vehicle is retuned to the base station upon connection of the system to the utility grid.

It is to be understood that the heater system 64 is also optional. Inclusion of the heater system provides the ability to maintain the target temperature of the cargo system when the target temperature is higher than the ambient temperature The heater 64 is provided in thermal communication with the cargo compartment 34 and in electrical communication with the controller 90. Systems which include a heater may also include a switch for placing the system in a “winter/cold weather” mode of operation. Such a switch may provide for deactivation of the evaporator system.

The system has been described as including first and second passageway coverings in connection with the first and second passageways 70, 72 of the partition wall 52. These passageway coverings can be provided by essentially any means for selectively opening and closing the first and second passageways 70, 72, for example, hinged doors or curtains. The curtains can, for example, be provided by free hanging strips of flexible material. In addition, as described in connection with the first passageway 70, the passageway covering can be provided by the cold plate fan 76.

Although the partition wall 52 of the refrigeration system 50 has been described and illustrated as including a first passageway 70 positioned near the roof structure 26 and a second passageway 72 near the floor structure 28, it is to be understood that it is not required for the passageways to be positioned in this manner. The passageways 70, 72 could, for example, be located on the left and right sides of the partition wall 52. When in the open positions therefore, air flow would be provided across the cold plate 80 in a direction from left to right or from right to left. It is also to be understood that the cold plate fan 76 could be positioned at the second passageway 72 rather than the first passageway 70. In this configuration, air would be drawn across the cold plate 80 in a direction opposite of that indicated by the arrows 92. It is also to be understood that it is not required that the partition wall is a rigid structure. Rather the partition wall 52 can be provided by any device which provides a thermal barrier. The partition wall 52 can, therefore, be provided by a thermal curtain.

One method of operating the controller has been described in connection with FIG. 3. It is to be understood that one of ordinary skill in the art could configure the controller to operate in variety of different manners to achieve the functionality described. For example, the order in which the controller performs the various steps can be modified. At steps 124, 134, and 136 the difference between the target temperature and the temperature of the cargo compartment or the difference between the set point and the temperature of the cargo compartment can be varied. For example, at step 134 is may be desirable to activate the cold pate air exchange operation until the temperature of the cargo compartment is two degrees below the target temperature rather than one degree below the target temperature. It is also to be understood that at steps 124, 134 and 136 for example, the cargo compartment temperature can be compared with either, the set points or the target temperature.

Finally, although the cold plate compartment and the cargo compartment have been described as being defined by the body of the vehicle, it is to be understood that the cold plate compartment can be located outside the body of the vehicle. For example, a cold plate compartment could be provided in front of the vehicle body and passageways could be provided through the front wall of the body to provided for the flow of air between the cold plate compartment and cargo compartment. 

The invention claimed is:
 1. A refrigeration system for use in a vehicle, the refrigeration system comprising: a cold plate compartment; a cold plate positioned within said cold plate compartment; a cargo compartment isolated from said cold plate compartment; a first passageway extending between said cold plate compartment and said cargo compartment; a second passageway extending between said cold plate compartment and said cargo compartment, a passageway covering for opening and closing said first and second passageways; wherein the temperature of said cargo compartment is lowered by opening said passageway covering and by providing air from said cold plate compartment to said cargo compartment through said first passageway and from cargo compartment to said cold plate compartment through said second passageway.
 2. The refrigeration system as defined in claim 1, further comprising: an isolation wall positioned between said cold plate compartment and said cargo compartment and wherein said first and second passageways are positioned within said isolation wall.
 3. The refrigeration system of claim 1, further comprising: a cold plate fan in communication with said first passageway, wherein said cold plate fan is operated to draw air across said cold plate and into said cargo compartment.
 4. The refrigeration system of claim 1, further comprising: a defrost system for defrosting said cold plate.
 5. The refrigeration system of claim 1, further comprising: a controller; an evaporation system in electrical communication with said controller; a cargo compartment access door; a cargo compartment access door switch in communication with said cargo compartment access door and in electrical communication with said controller; and wherein when said cargo compartment access door is opened, said cargo compartment access door switch provides a signal to said controller, in response to said signal provided by said switch said controller provides a signal to said evaporation system to turn off said evaporation system.
 6. The refrigeration system of claim 1, further comprising: a controller; a recirculation fan positioned within said cargo compartment and in electrical communication with said controller; a cargo compartment access door; a cargo compartment access door switch in communication with said cargo compartment access door and in electrical communication with said controller; and wherein when said cargo compartment access door is opened, said cargo compartment access door switch provides a signal to said controller, in response to said signal provided by said switch said controller provides a signal to said recirculation fan to turn off said recirculation fan.
 7. The refrigeration system as defined in claim 1, further comprising: a controller for receiving a user defined target temperature of said cargo compartment; and a temperature sensor for providing cargo compartment temperature data to said controller.
 8. The refrigeration system as defined in claim 7, further comprising: a cold plate fan in communication with said first passageway, wherein when said controller receives temperature data indicating the temperature of said cargo compartment is higher than said target temperature, said controller provides a signal to said cold plate fan to activate said cold plate fan.
 9. The refrigeration system of claim 7, further comprising: a heater in electrical communication with said controller and in communication with said cargo compartment; wherein when said temperature data indicates that the temperature of said cargo compartment is lower than said target temperature, said controller provides a signal to said heater to activate said heater.
 10. The refrigeration system of claim 1, further comprising a defrost system in communication with said cold plate for defrosting said cold plate.
 11. The refrigeration system of claim 1, wherein said passageway covering is provided by a first passageway covering for opening and closing said first passageway and a second passageway covering for opening and closing said second passageway.
 12. A method of maintaining the temperature of a cargo compartment of a vehicle comprising the steps of: providing a cold plate compartment isolated from the cargo compartment having a cold plate therein; providing a first passageway between the cargo compartment and the cold plate compartment; providing a second passageway between the cargo compartment and the cold plate compartment; providing a first passageway covering; providing a second passageway covering; monitoring the temperature of the cargo compartment to determine whether the cargo compartment is to be cooled; upon determining that the cargo compartment is to be cooled, opening said first and second passageway coverings and providing air from said cold plate compartment to said cargo compartment and providing air from said cargo compartment to said cold plate compartment.
 13. The method of claim 12, further comprising the steps of: providing a controller.
 14. The method of claim 13, further comprising the steps of providing a cold plate fan in communication with said first passageway; and upon determining said cargo compartment is to be cooled, providing a signal from said controller to activate said cold plate fan.
 15. The method of claim 13, further comprising the steps of: providing a user defined target temperature of said cargo compartment to said controller; and; wherein said step of monitoring the temperature of said cargo compartment is providing by a temperature sensor positioned in said cargo compartment and in communication with said controller.
 16. The method of claim 13, further comprising the steps of: providing a cargo compartment access door switch in communication with a cargo compartment access door and said controller; and wherein when the cargo compartment door is opened, said cargo compartment access door switch provides a signal to said controller to deactivate said cold plate fan.
 17. The method of claim 16, further comprising the steps of: providing a recirculation fan in communication with said cargo compartment and in communication with said controller; and wherein when the cargo compartment door is opened, said cargo compartment access door switch provides a signal to said controller to deactivate said recirculation fan.
 18. The method of claim 13, further comprising the step of: providing a defrost system in communication with said controller and said cold plate; and providing a signal to said defrost system to activate said defrost system. 